Gun turret sighting compensation



"N mam mm 333-2399 OR 2,408,681 SP3 Oct. 1, 1946. G. w. PONTIUS, 30., ETAL 2,408,681

GUN TURRET SIGHTING COMPENSATION SYSTEM Filed April 9, 1942 12 Sheets-Sheet 1 INVE ToRs afia mew 'RANK v. K'uzMn'z Y B .u)?

A TTORNE 3 M t W' AL i we x n u m LN u u.

1946. G. w. PONTIUS, 30., ETAL 2,408,681

GUN TURRET SIGHTING COMPENSATION SYSTEM Filed April 9, 1942 12 Sheets-Sheet 2 IIIIIIIIIIIIIIIIIIIIIII/? INVENTORS GEORGE. W- PONTIUS ARTHUR P. WILSON FRANK V-KUZMITZ G. w. PONTIUS, 313., EI'AL 2,408,681

GUN TURRET SIGHTING COMPENSATION SYSTEM Filed April 9, 1942 12 Sheets-Sheet 3 INVENTORS GEORGE w PONTIUS '6 ARTHUR P. WILSON FRANK V. KuzMrrz PUNK E53; HUIHLI? I\J| Oct. 1, 1946. G. w. PONTIUS, 30., EI'AL 2,408,681

GUN TURRET SIGHTING COMPENSATION SYSTEM Filed April 9, 1942 12 Sheets-Sheet 4 INVENTORS GEOR ARTH R P W\LSON FRANK \LKUZMH'Z I ATTORNEY E wmom'ms 1 PONTiUS P. wmsou v. xu MITZ ATTORNEY.

l2 Sheets-Sheet 6 "H" HAIR MOVEMENTS AT 150 ZENrrH FIGJ4 I G. w. PONTIUS, 30., ETAL GUN TURRET SIGHTING COMPENSATION SYSTEM Filed April 9, 1.942 7 77 C4-COM P07 Oct. 1, 1946.

"VIIHAIR MOVEMENTS AT \60ZEN!TH C5 I60 ZENITH gf qjw mm numumm Oct. 1, 1946. G. w. PONTIUS, 30., ETAL 2,408,681

GUN TURRET SIGHTlNG COMPENSATION SYSTEM Filed April 9, 1942 12 Sheets-Sheet '7 154 was can on vao'cnn INVENTORS GEORGE \rv.s='oN'nu5 Z 7 BY PZRWW-ih??? T ORNE Y 1, 1946. 5. w. PONTIUS, 30., ETAL 2,408,681

GUN TURRET SIGHTING COMPENSATION SYSTEM A Filed April 9, 1942 12 Sheets- Sheet 8 ATTORNEY W L M m Oct. 1, 1946.

G. W. PONTIUS, 3D., EI'AL GUN TURRET SIGHTING COMPENSATION SYSTEM Filed April 9, 1942 12 Sheets-Sheet 9 FIGJB INVENTORS GEORGE W- PONTlUS' ARTHUR P. WILSON FRIXNK V- KUZMITZ A TTOHNE Y if. HOME? HZLJM 11 m 1 mum m m 1946. G. w. PONTIUS, an, El'ALl 2,408,681

GUN TURRET SIGHTING COMPENSATION SYSTEM Filed April 9, v1942 l2 Sheets-Sheet l0 \NVENTORS GEORGE NPONTIU5 ARTHUR P WILSON BY FRANK V- KUZVHTZ GEOMURHJM INS 1 RUMEN IE.

Oct. 1, 1946. G. w. PONTIUS, 30., ETAL 2,403,681

GUN TURRET SIGHTING COMPENSATION SYSTEM Filed April 9, 1942 12 Sheets-Sheet 11 INVENTORS m GEORGE W. PONHUS ARTHUR P- WlLSON BY FRANK \LKUZNHTZ I GEM-41E? mm m1; 1 iiUiVEtN x Oct. 1, 1946. G. w. PONTIUS, 30., ETAL 2,408,681

GUN TURHET SIGHTING COMPENSATION SYSTEM Filed April 9, 1942 12 Sheets-Sheet l2 INVENTORS m; GEORGE W. PON'T'lUS ARTHUR P \NiLSON FRANK V.KUZM\TZ ATTO Patented Oct. 1, 1946 GUN TURRET SIGHTING COMPENSATION SYSTEM George W. Pontius, III, Arthur P. Wilson, and Frank V. Kuzmitz, South Bend, Ind.

Application April 9, 1942, Serial No. 438,236

13 Claims. 1

This invention relates to gun turrets and more particularly to a. sight for aircraft gun turrets wherein compensation is made for: (1) the ballistics deflection of a projectile; and (2) lead with respect to a relatively moving target.

The invention will be described as applied to gun turrets for the upper and lower surfaces of an airplane, although it is not limited to such applications. A lower turret to which the invention is applied is described more completely in gongilus application Serial No. 391,911 filed May It is an object of the invention to provide a sighting device for guns which indicates lead on a target.

It is another object of the invention to provide a sighting device for guns which corrects for the deflection of a projectile caused by windage, gravity and magnus effect.

It is another object to provide a sighting device which makes a single correction combining lead and ballistics deflections.

It is another object to provide a sight in the field of an optical instrument wherein cross hairs or other reference media move relative to the field of an optical instrument to give an automatic correction.

It is an object to provide an automatic ballistic correction system for sights wherein the correction is obtained from electrical bridges dependent upon the position of the guns in their field of fire.

Other objects and advantages of the invention will be apparent from the following specification and drawings in which:

Figure 1 is a side view of an airplane having a lower turret in a retracted position and having a sight compensation system or mechanism made according to the present invention;

Figure 2 is an enlarged sectional view of the airplane of Figure 1 in the region of the lower turret, showing the turret in an extended or operative position and being at the instant controlled and fired by a gunner;

Figure 3 is an isometric, schematic sketch of the lower turret in an extended position, partly in section and showing the mechanical parts and movements;

Figure 4 is a view in vertical section, partly schematic, of a periscope of the lower turret, showing the path taken through the periscope by light rays reflected horizontally from an object;

Figure 5 is a fragmentary view in elevation of a detail of the adjustable fastening means for holding the erector lens housing;

Figure 6 is a schematic view showing the path taken through the periscope by light rays reflected vertically from an object;

Figure 7 is a schematic drawing to illustrate the various images of target airplanes seen by the gunner at the respective positions of the target airplanes with relation to the airplane in which the turret is mounted;

Figure 8 is a view in vertical section through the sight box or bottom part of the periscope of Figure 4, showing the parts and their relation in more detail;

Figure 9 is a sectional view showing the top of the sight box along the line 9-9 of Figure 8;

Figure 10 is an isometric view of the cross hair mechanism of the sight box and the actuating galvanometers therefor as well as the position of the periscope mirror, as seen from above and from the right with reference to Figure 9;

Figure 11 is an isometric view of the periscope prism mounting, with part of the sight box housing broken away as well as part of the prism housing to show the details of construction;

Figure 12 is a diagram showing correction angles for lateral deflections of a bullet for various points in a portion of the hemisphere of fire of the lower turret;

Figure 13 is a diagram illustrating an electrical cam producing a voltage curve corresponding to the correction angles for lateral deflection of Figure 12 for any given point on the herispherical field of the lower turret and used in the sight correction system for the turret;

Figure 14 is a diagram illustrating the correction movements of the cross hairs of the lower turret for various azimuth positions of the turret when the guns are pointing straight down at zenith;

Figure 15 is a diagram of an electrical cam for producing a voltage curve corresponding to the correction movements of the horizontal cross hair shown in Figure 14;

Figure 16 is a diagram of the correction angles for the vertical deflections of a bullet for various points in the hemisphere of fire of the lower turret;

Figure 1'7 is a diagram of an electrical circuit forming electrical cams and producing a voltage curve corresponding to the correction angles for vertical deflection of Figure 14 and 16 for vertical deflection for any given point on the hemispherical field of fire of the turret;

Figure 18 is a, phantom view showing the lower turret in dotted lines and having superimposed thereon the complete sight correction circuit for moving the cross hairs of the periscope, and including the electrical cams of Figures 13, 15 and 17;

Figure 19 is a perspective view of an airplane having an upper turret including a compensated sight made in accordance with the invention;

Figure 20 is a vertical section through the airplane of Figure 19 and the canopy of the turret showing a gunner operating the turret with the guns pointed toward the rear of the airplane;

Figure 21 is an isometric projection of the mechanical parts and movements of the upper turret;

Figure 22 is an elevational view in section of the periscope of the upper turret showing the path of light rays therethrough;

Figure 23 is a view of the prism, lens and mirror of the periscope showing the paths taken by rays of light from a vertical direction;

Figure 24 is an isometric view of the galvanometers controlling the cross hairs of the sighting mechanism included in the periscope, and showing the periscope mirror; and

Figure 25 is a phantom view of the upper turret in broken outline having superimposed thereon in full lines the complete electrical compensation circuit.

The placement of the lower turret in an airplane is shown in Figure 1. Airplane I retains a turret I 02 in a retracted position in the bottom of the fuselage. When thus retracted the bottom of the turret is substantially flush with the surface of the fuselage and offers little resistance to the airstream.

The turret I02 is shown on an enlarged scale in an extended position in Figure 2. A gunner I04 kneels on a cushion I06, his chest supported on a rest I08 attached to the turret. The gunner looks through a periscope in the turret to sight the guns, and with his right hand operates the electrical power controls for the movements of the turrets and guns, while with his left hand he operates a trigger control. Gun wells II2 are provided in the airplane I00 at the rear of the turret as a housing for the guns when the turret is retracted, at which times the guns III] will be horizontal.

The mechanical parts relating to the movement of the turret are shown in diagrammatic form in Figure 3 wherein the turret is shown in an extended position. The turret I02 as a whole is supported on a four-armed spider I I4 which is secured to structural members such as II of the airplane I00, and which has a central collar I I6. Ball bearings such as H8 rotatably support an internally threaded sleeve I20 within collar II6, which sleeve has an upper ring gear portion I22. A threaded column I24 is threaded into sleeve I20 and is thereby supported within spider II 4. A head unit I26 rotatably rides on the upper end of column I24 and is itself restrained from rotation by a telescoping yoke member I28 secured to the outer end of one arm of spider I I4.

A single power source is used to rotate the sleeve I20 in order to rotate the turret in azimuth or optionally to retract and extend the turret. This power source is an electric motor I30 suitably secured to the spider H4. The motor I30 drives a motor shaft I34 to which is secured a worm I36. Worm I36 engages a worm wheel I38 which is secured to a drive shaft I40 journalled in suitable bearings which will be later described. A worm I42 on shaft I40 engages ring gear I22, causing the sleeve I 20 to rotate within central collar II 6, When electric motor I30 is operated.

The motor I30 can be reversed by reversing the field current, thus reversing the direction of rotation of sleeve I20. The gear train provides a large reduction in rotation allowing the use of a very high speed motor, to provide a high power to weight ratio.

Also shown in Figure 3 is a shaft I40 driven by motor worm wheel I38 and having a worm I5I on the other end thereof. Worm I 5I drives a worm wheel 604 which in turn drives a compensator shaft 602 having a series of electrical cam followers secured thereto and adapted to contact electrical compensation cams encased in a housing 6 I0 as shown in Figures 3 and 18. The gear reduction at worm I5I is the same as that of driving worm I42 at the column resulting in compensator shaft 602 making a complete rotation for every rotation of column I24. In other words, the movement of electrical cams in housing 6I0 is synchronized with the azimuth movement of the turret.

The column I24, and thereby the turret also, may be rotated in azimuth or retracted and/or extended, by selectively connecting column I24 with sleeve I20 or with non-rotatable head I26. This selective connection is performed by an L- shaped key I44 held in a hole through column I24 and selectively engaging an internal notch I50 in sleeve I20, or an external notch I52 in non-rotatable head I26. The mechanism for moving key I44 has been completely described and claimed in Pontius et a1. application Serial No. 407,468, filed August 19, 1941, entitled Gun turret.

When key I44 engages notch I52 in non-rotatable head I26, column I24 is restrained from rotation. If motor I30 now rotates ring gear I22, and thereby sleeve I20, the column I24 will be raised or lowered according to the direction of rotation of sleeve I22. The head I26 is lowered or raised with column I24, and the yoke member I28 will telescope and extend and will act at all times to keep head I 26 from rotating. In this way the extension and retraction of turret I02 is accomplished. When the turret I02 is extended the key I44 may be moved to engage notch I50 in sleeve I20 and the column I24 will rotate as sleeve I20 rotates, and thus provide the operative movement of rotation in azimuth. It will be noted that in such case the key I44 will be out of notch I52 and there is no restriction on the movement in azimuth. The column I24 can be rotated continuously in either direction for any given number of rotations.

Certain parts of the turret are fastened on the lower end of column I24. These parts include a rotatable shaft I56 to which the guns III] are secured. The details of construction for aflixing the guns to shaft I56 has been described, Pontius application Serial No. 391,911, filed May 5, 1941, entitled Gun turret. A worm wheel sector I 60 is secured to shaft I56 and is engaged by a worm I'62 fastened to a drive shaft I64. Drive shaft I64 in turn is driven by a worm wheel I66 secured thereto, which is driven by a worm I68 secured to a motor shaft "0 of an electric elevation motor I12. The driving mechanism described is preferably positioned within a frame or housing which will be described later.

Also shown in Figure 3 is an elevation gearing system for electrical compensation cams. Connected to motor worm wheel I66 is a shaft III having a worm II'Ia secured to the outer end thereof. Worm I'I'Ia drives a compensator worm wheel 6|2 which is secured to a compensaiJLUl'i'Ii; l lupin.

tor shaft 6I4. Fastened to the end of shaft GM is a zenith electrical cam in housing 6I6. The gear reduction at worm II'Ia is not the same as at worm wheel sector I60, and shaft 6I4 rotates approximately three times faster than gun shaft I56 but in synchronism with it. This is permissible since the greatest movement of the guns in zenith is about 95, and the increased movement of shaft 6I2 gives greater sensitivity.

The elevating gear train and its actuating motor are adapted to elevate or depress the guns, depending upon the direction of rotation of motor I12, which is reversed by reversing the field. The guns IIO can be elevated above horizontal as far as is permitted by the shape of the airplane in which the turret is mounted, and can be depressed to point straight down. The zenith are as will be described for purposes of illustration, will be limited to a 90 are from horizontal to straight down.

The mechanism for synchronizing .the periscope of the turret with the guns is also shown in diagrammatic form in Figure 3. A pinion I90 is secured to shaft I56, and engages a rack I92 on the upper end of a bar I94, suitably positioned by means which will later be described. A rack I96 on the lower end of bar I94 engages a gear sector I98 secured to a shaft 200 which rotatably supports a prism 30I forming a part of the optical system of the periscope. When guns IIO are elevated or depressed by rotating with shaft I56, the prism will be rotated, not an equal amount, but in proportion thereto, thus synchronizing .the line of sight of the periscope with the direction in which the guns point.

The periscope system 300 of the turret is shown in Figures 4 through '7, and is shown in longitudinal section in Figure 4. The periscope comprises in the main a periscope tube 306, and a sight box 302. The periscope tube 306 is formed in three pieces. At the top is an eyepiece tube 3I0 retaining eyepiece lenses 3I2 and 3I4. Eyepiece tube 3 I rotates within cushion 304 on bearings 3| I, which insure that there will be no binding of the two parts.

The lower portion of periscope tube 306 comprises an upper spacer member 3I6 and a lower spacer member 3I8 in each of which there are positioned lenses having an erector function to invert the image to an upright or normal position for views directly to the rear of the airplane. The upper end of spacer member 3I6 retains a plate glass piece 320 on the bottom side of which is focused the image viewed by the eyepiece lenses 3I2 nd 3I4. A lens 322 is also placed near the upper end of spacer tube 3I6 and helps to focus the image on the bottom of plate 320. The lower spacer tube 3I8 retains erector lenses 324 which are held by snap rings 325 in a perforated housing 326 secured to the upper end of spacer member 3I8. Housing 326 is held in lower spacer tube 3 I8 by screws 32! fitting in longitudinal slots 328 in tube 3I8, as shown in detail in Figure 5. Slots 328 allow adjustment of the erector housing 326. Lower spacer tube 3I8 also retains a fixed diaphragm or stop 329 for eliminating ambient; rays of light. The lower end of spacer tube 3I8 is screwed into sight box 302.

The sight box 302 is also shown in longitudinal section in Figure 4. It includes the rotatable prism 30I whose transverse section is that of an isosceles right triangle. Light entering prism 30I is refracted and reflected into a compound objective lens 330. Objective lens 330 is made up of two plano-convex lenses with a spaced intop of the image seen by the gunner.

termediate double-concave lens of material having a different index of refraction from the outer lenses, to form an achromatic lens group. A diaphragm or stop 33I is placed over the outer side of lens 330 to stop ambient light from entering that lens.

Light which passes through lens 330 from prism 30! is reflected by a mirror 332 placed at an angle of to the axis of the objective lens 330 and to the axis of the periscope tube 306. The light so reflected forms an image in the plane I--I, just above the mirror 332. Two lenses 340 are placed in sight box 302 above this image plane and they help to bend light rays passing through them from the image to the erector lenses 324.

The path taken by rays of light is shown in Figure 4. The ray T represents a ray on the upper side or top of the cone of the field of the periscope system, which cone has an angle of approximately 40 or greater. Ray 0 represents a horizontal center ray in the field cone, and ray B represents a bottom ray in the field cone. The window surface A'B of the prism 30I refracts all of these rays to the hypotenuse surface AC' where they are reflected and then refracted out of the prism at one end of the surface 0'3, and into the objective lens 330. The fixed diaphragm 33I is placed over the outer surface of the planeconvex lens nearest the prism, causing all rays of light that enter the lens 330 to cross in or near the outer lens. The objective lens 330 causes the rays of light to form an image, and because of the interposition of mirror 332, this image is formed in a plane parallel to the axis of objective lens 330.

Assuming that the sight box 302 is pointed toward the rear of the airplane I00, the gunner will be crouched facing toward the rear also, as in Figure 2. If there were no lenses in periscope tube 306, the image on plane I--I would appear upside down to the gunner on plane I-I since the ray T will be at the left in Figure 4, and therefore to the bottom of the gunners image, and the ray B will be at the right in Figure 4, or to the In order to make this image appear right side up, or

erected, erector lenses 324 are interposed between image II and the eyepiece 3I0. Erector lenses 324, with the aid of lenses 340 and 322 form an erect image of the objects to the rear, in the plane I2I2. The ray T is to the right or the top of the image seen by the gunner in plane I2I2, and ray B is to the left, or to the bottom in plane 12-12. The eyepiece takes rays from the image I2I2 and concentrates them for the gunners eye at the top of the cushion 304 where the gunners head will be resting. It will be noted that the convergence of the rays at the top of the eyepiece is at an angle approximately equal to that of the field rays T and B, resulting in practically no magnification of the image which gives a natural size image, allowing the gunner to estimate the range of a target.

Figure 6 shows the prism 30I in the other extreme position, taking in a vertical cone of field. As in Figure 4, the prism 30I will refract and reflect the light into the lens 330 which condenses it for forming an image on the plane II, Figure 6 shows the path of light for this straight down position, as compared to Figure 4 which shows it for the horizontal position. Any intermediate position of the prism 30I would give rays of light in paths intermediate those shown in Figures 4 and 6.

The periscope of this application with a field of about 45 gives a larger field than prior periscopes designed for gunfire which have fields not to exceed 30. The larger field obtained by the present periscope is due first, to an objective lens that will take in at least a field of 45, and second, to a prism that will transmit a 45 field to such a lens at all positions of rotation and at the same time give an exit pupil not less than /4" in diameter without transmitting double images. The lens must have a relatively short focal length and relatively wide angle of field, and must be well corrected over this field when the image produced by this lens is used for compensation. Camera lenses of relatively short focal lengths have been found satisfactory for this purpose because of their wider angles and well corrected small images which in turn desirably limits the diameter of the tube.

The prism 30! must be relatively large as compared to those in use in prior periscopes. A three inch prism, for example, is required in the present periscope. The shaft about which the prism rotates must be placed so that when the prism rotates the prism will be as close as possible to the lens 330. This placement of the axis of rotation is very important as otherwise the prism cannot transmit the necessary field to the lens. The placement of the pivot shaft for the prism with regard to synchronism with the guns is unimportant as long as the prism rotates near lens 330. All that is required, once a given position of the prism is found to include a field into the center of which the guns will fire, is that the prism will rotate only one-half as much as the guns rotate in elevation above or below such a position. This limitation to one-half the rotation of the guns is due to the mirror function of the prism, wherein the included angle of reflection of a fixed ray of light will increase or decrease twice as much as the angle the mirror surface itself is rotated.

The sight box 302 also retains two movable cross hairs for sighting purposes, the details of which will be described later. Both cross hairs are in the image plane I--I, so that they will appear to be a part of the image viewed by the gunner, and will not appear to move if the gunner should move his head about on the cushion 304. One cross hair appears to be vertical in an upright field, and the other appears to be horizontal in an upright field. They are both movable laterally to their axes by automatic electrical means for ballistic corrections, and thus move about on the round image field viewed by the gunner.

The plate glass member 320 has a dot DC impressed in its center for orienting the initial position of the cross hairs relative to the field. There is also a dot DT impressed on plate glass 320 which would appear to be on the upper part of the vertical hair when the hair is in a normal position and the fieldis toward the rear of the plane. This dot is to relate the turret to the cross hairs so that the gunner will know which way to move the turret to train the cross hairs on the target.

It will be noted that a passage 34! in the upper part of sight box 302 communicates the right hand part of the sight box with the periscope tube 306, and that a passage 342 communicating said right hand part of the sight box with the left part of the sight box. These passages and the holes formed through perforated housing 326 allows the communication of air between the sight box 302 and the tube 306. By providing a water absorbing cell or unit in the sight box, which cell will be described later, the major part of the periscope can be dehydrated to prevent the condensation of moisture on the optical pieces as they become chilled due to climatic or altitudinal changes in temperature. Elimination of condensation is very important and the means just described to eliminate condensation forms a feature of the invention.

The views of an object as seen by the gunner through the periscope are shown in Figure 7. The gunner !04 is shown in a top view looking down the periscope as he crouches facing toward the rear of the plane. Target airplanes 344 flying in the horizontal plane including the sight box of the periscope in the middle thereof are shown in four positions: to the rear (to the right in Figure '7) to the side toward the gunners left (top in Figure '7); to the front of the plane (left in Figure 7) and to the side toward the gunners right (bottom in Figure '7). The view the gunher would see if the periscope were properly orientated in each case is opposite each of the target airplanes 344, and is a round field having a side view of the airplanes 344 therein. The cross h'airs are in the middle of the field, and the orientation dot DT appears to be on the vertical cross hair in every case.

It will be noted that the only upright or exact image relative to the gunner himself is at the rear of the airplane. As he looks at the airplane to his left the target airplane 344 appears to stand on its nose. Likewise, the target airplane to the front of the plane appears to be upside down relative to the gunner, and the airplane to his right appears to be standing on its tail. In every View, however, the orientation dot DT indicates to the gunner the true position and direction of flight of the target airplane relative to the cross hairs and the field. From this it is apparent that the gunner must not aim and fire the gun relative to himself as he would be hopelessly confused by the various positions and directions that a target plane would assume for a given cross hair position of the target on the field. The gunner must completely detach himself from consideration, and follow the target and aim the guns by association of the target with dot DT in the field. The gunner will train himself to a given muscular reaction for a given position and direction of the target in the field, regardless of the direction in which the guns are pointed with relation to the airplane in which they are mounted. The erector lenses are provided chiefly for conventional reasons and also because the most important job which this gunner has is to protect against an attack from the rear.

The details of construction of the sight box 302 are shown in Figures 8, 9, 10 and 11. The sight box itself is divided into two main parts, a hood 350 for the prism 30!, and an image box 352. These two parts are separated by a wall 35!, which wall also supports the objective lens 330 and has the de-hydrating hole 342. The prism 30! is mounted on shaft 200, as is shown generally in Figure 3 but specifically as is shown in more detail in Figures 9 and 11. In Figures 8 and 11 it will be noted that shaft 200 supports prism 30! by means of a housing 354 which covers the top and the sides of prism 30!. The prism 30! is held in the housing 354 by a clamp bar 356 which presses a notched rubber cushion 358 against the apex of the prism 30! (Figure 8). Shoulders 355 (Figure 11) contact the upper eo. crowlrlmo/ll. lrlemll /ltl\ll&

edges of prism 3M and thereby hold the prism without danger of scratching the central part of the upper surface which is the reflector surface A'C of the prism. Shaft 200, as shown in Figure 9, is essentially two stubs screwed into housing 354 and journalled in hood 358.

The details of construction of the gear sector I98 which rotates prism shaft 200 are also shown in detail in Figures 9 and 11. As already explained, the prism 30I needs to rotate only onehalf as much as the guns III) are elevated or depressed to be in synchronism with them, because of the mirror function of the prism. As shown in Figure 3, the gear sector is of twice the radius (and consequently sector circumference) as the driving gear I90 on gun shaft I56, thus providing a 2 to 1 reduction in rotation. Referring to Figure 11, it is pointed out that gear sector I98 is mounted freely on shaft 200, but drives it through an adjustment member I99 secured to shaft 200 and haVing adjustment screws 2UI bearing on sector I98. This arrangement of parts allows for the very minute adjustments necessary to synchronize the prism 3! with the uns IIO.

A piece of flexible opaque sheeting 360 (Figure 8) of leather or rubber is attached to housing 358 by clamping against cushion 358 by clamp bar 356. The other end is fastened by screws to wall 35I. Sheeting 360 prevents light from directly entering lens 330 or the face B'C' of prism 30I.

Hood 350 is closed by a window of glass 362 clamped against a gasket 364 by a rim 366 screwed to hood 350. All rays of light entering the periscope must pass through this window, and for this purpose it must be large enough to pass a full field to the prism 30I for all positions of rotation.

The details of construction of the cross hairs are shown best in Figure 10. Two permanent magnets 316 of horseshoe shape, each has a rotor 312 of any well known construction such as are used in galvanometers. Each rotor is attached to a U-shaped member 314 having a fine metal cross hair wire 316 across the upper ends. The U-members 314 with rotor attached are suitably supported on each end by hardened, pointed pins 318 journalled in a recess in hardened heads 380 held in image box 352. Electric current is supplied to the galvanometer units by wires leading from socket 211 (Figure 8) which wires are connected as shown in Figure 10 to hair springs 382 (only two of which are seen) at the journals for both U-members 314. Current flows into one hair spring, goes through the associated rotor 312 and through the bottom leg of U- member 314 to the other hair spring where the current leaves the member. Hair sprin s 382 help to center the U-members 314 as well as pass current through the rotors 312. The journals and hair springs at the rotor end of the U-members are not shown, but they are of the same construction as those shown. It will be noted that one leg of one U-member is curved over part of its length to accommodate the casing of objective lens 330. Counterweights 384 help to balance the U-members.

Referring still to Figure 8 it may be seen that the mirror 332 is mounted on a standard 334 attached to the bottom of image box 352. The mirror reflects the light rays so that an image is formed in plane I-I just above it. It will be noted that the cross hairs 316 are very near this plane so that they appear to be a part of the image viewed by the gunner.

The cross hairs are placed at right angles to each other, and can move either side of dead center, depending upon the direction of the current going through rotors 312. The magnitude of the movement depends upon the voltage across rotors 312. These two factors, magnitude and direction of the current, cause the cross hairs to move independently and to move relative to the field of the periscope, in correcting for ballistics deflection and lead. The gunner has merely to move the turret and guns so that the intersection of the cross hairs is superimposed on the image of the point on the target which he desires to hit. The electrical circuit and its parts for moving these cross hairs will be later described.

As shown in Figures 8 and 9, a tubular cell of screen or perforated metal 386 is screwed into the bottom of image box 350. This cell is filled with silica gel, calcium chloride, or other moisture absorbent material and is used to de-hydrate the periscope. Water vapor can pass through perforated housing 326 (Figure 4) to cell 386. In this manner the major part of the periscope can be rid of water vapor and thus freedom from condensation on the optical system is assured.

Having explained the nature of the turret and the sighting device, the sight compensation will now be explained. As explained with reference to the periscope in Figures 8 and 10, the cross hairs 316 move with relation to the field of the periscope and the point of intersection of the two when superimposed on the image of the target in the periscope will represent a condition of the guns whereby they are so compensated that when fired the projectiles will strike the target at a point corresponding to the image point as seen in the periscope. The electrical system for passing current through the rotors 312 (Figure 10) of the galvanometers to move the cross hairs is entirely independent of the power current and circuits and has its own source of power and ground wires.

Ir a target were stationary and if the trajectory of projectiles were on the exact line of the axis of the gun barrels, there would be no need for sight correction. In all firing however, the effect of gravity causes the bullet to drop from the path of the axis of the gun toward the center of the earth. Also if a wind is blowing at an angle to the axis of the gun barrel, the bullet will be blown up or down or sideways depending upon the direction of the relative wind. If the relative wind is of any appreciable velocity it causes magnus effect, 1. e., the tendency of the bullet to rise or fall from its normal path depending upon the direction of the wind. The magnus phenomenon is caused by the formation of a low pressure area on a part of a spinning object when moving through a transverse wind, causing the object to rise or fall depending upon the direction of the wind with relation to the spin of the object. Still another consideration in sighting a gun is lead; 1. e., the amount in front of a moving target that a gun must be aimed in order to hit the target considering the time consumed in trigger actuation and flight of the bullet to the target.

The compensation system shown in this application is designed to compensate for all the predictable factors affecting the deviation of a bullet from the axis of the gun from which it is fired. The factors for which there is compensation include lead, magnus eifect, gravity effect, and windage deviations.

Since the deviation of a bullet from the axis of its gun usually increases with the distance it travels, the corrections must be determined for a definite range, because corrections effective for all ranges would involve prohibitive complications of the correcting system. Rather, it is more expedient to choose the range at which most of the shooting can be done with relation to the calibre and type of gun used. For a .50 calibre machine gun this range is preferably about 600 yards. If the target is at a point inside this range the over corrections will not cause appreciable inaccuracies, for although there will be error, the target is closer and will intercept a larger angle of fire than a more distant target. For targets at a range greater than that chosen the guns may not be effective. Therefore the gunner will not normally shoot at such ranges and the errors are of little importance.

The deflection of the bullets from the axis of the guns, caused by gravity, magnus effect and windage are herein called ballistic deflection. Such deflection is preferably determined by empirical methods. The deflection data are then reduced pictorially by means of graphs and curves and broken down into elements of azimuth and zenith measurements to correspond with the mechanical movements of the guns in the turret, and the sight compensation system is designed accordingly. In operation, electrical currents are sent to the rotors 312 of the galvanometers, depending generally upon the position of the guns in zenith and azimuth, and the cross hairs 316 are moved automatically an amount depending upon the position in zenith and azimuth.

The relative lead of a gun upon a moving target with respect to the gun is a direct function of the. speed of the target, and, where trigger actuation may be considered to be practically instantaneous, of the speed of the bullet or projectile. For a given gun the projectile speed is substantially constant and the relative speed of the target need be the only variable correction. In the present turret an electrical current responsive to the speed of the target is obtained by generators geared to or mounted on the shafts of the zenith and azimuth motors. Inasmuch as the turret must be moved to keep the target in the periscopic field, the rotation of the motors which move the turret and guns will directly reflect speed of the target, and therefore reflect the lead in azimuth and zenith. This lead current is sent to the galvanometer rotors 312 and is superimposed on the correction current for windage, magnus effect and gravity as described above.

The ballistics deflection of the guns of the turret, which deflection is the algebraic summation of the effects of windage, magnus effect and gravity, can best be broken up into vertical and lateral components with respect to the airplane in which the turret is mounted. The lateral deflections are corrected by advancing or retarding the rotation of the turret in azimuth which advances or retards the axis of the guns with relation to the target. The vertical deflections are corrected by elevating or depressing the guns of the turret with relation to the target.

These lateral and vertical components of ballistics deflection are correlated with the movement of the cross hairs 316 of the periscope. As shown in Figure 7, and as explained with reference thereto, the cross hairs intersect the field of the periscope vertically and horizontally. As best shown in the right hand field diagram of Figure 7, which is at the rear and is an upright image with respect to the gunner, the cross hair which intersects the gunners image up and down is the vertical cross hair, and the hair that intersects the image from the gunners left to right is the horizontal cross hair.

These hairs can be correlated with the rays of light of Figure 6, the cross hair intersecting the upper ray T and the lower B in the image plane I-I being the vertical hair and the other being the horizontal hair. Thus the hair parallel to the axes of the guns is the vertical hair hereafter designated as V and the hair transverse to the axes of the guns is the horizontal hair designated hereafter as H. From the foregoing it is evident that the V hair corrects for lateral ballistics deflections because it moves sideways and that the H hair corrects for vertical ballistics deflection because it moves up and down with regard to the image.

Before describing the lateral and vertical ballistic deflections of the bullets the terminology used herein expressing the correlated azimuth and elevation positions will be explained. Azimuth is expressed in degrees of a full 360 circle, with 0 as straight forward and the angular measurement being clockwise when looking down on the airplane. Thus when the turret is pointing at 0 azimuth it is pointing straight forward, at 90 it is to the right, at 180 to the rear and at 270 to the left. Zenith is expressed in terms of degrees of a half circle with 0 as straight up. Thus if the upper turret of an airplane be at 0 zenith it would be pointing straight up and if pointed at 90 would be horizontal. When the lower turret is pointing at horizontal it is at 90 zenith and when pointing straight down it is at 180 zenith. It will be remembered that the zenith arc of the lower turret is from 90 to 180 i. e. from horizontal to straight down.

Lateral ballistic corrections The correction for lateral ballistic deflection of a bullet is shown diagrammatically in Figure 12. The airplane I00 in which the turret is mounted is shown in the center of its range circle Cl which may be taken at 600 yards, assuming that the turret has .50 calibre machine guns. The 0 mark of the circle CI in azimuth is straight ahead as explained before.

The airplane can be assumed to be flying straight ahead, for example at 250 miles per hour. A target airplane TI is assumed to be traveling in .the same horizontal plane as airplane I00 and straight ahead at 250 miles per hour to remove considerations of lead from the ballistics compensation. If the guns were pointed straight at the airplane Tl the projectiles would not hit it. The 250 miles per hour wind would blow the bullet laterally backwards. (Magnus effect and gravity doo not cause lateral deflections at 90 zenith. The vertical error of magnus and gravity does not show in Figure 12 and will be considered later.) To correct for the lateral deflection with regard to plane TI the turret must be rotated so that the guns point in advance of the target Tl by an angle Al. The wind will blow the bullets backward and they will travel in the dotted path from airplane I00 to airplane TI and hit airplane Tl squarely,

The size of the angle Al for each position of the target plane TI is indicated by the length of the radial lines AI between the range line Cl and the lighter zenith line or curve C2. The

as. swarms/u. HtSHiUli IEN iii.

length of these lines, as will be appreciated, are merely a linear measurement of an angular quantity and therefore have no measurement value except relative or as compared to a scale. No scale is given however, as this description is merely qualitative and the data varies for various guns and is elsewhere available. By regarding these radial lines as relative measurements only, it will be noted that the lateral deflection at 90 zenith is greater at 90 azimuth than at 45 azimuth, and that at and 180 in azimuth the deflection is zero because bullets fired at those azimuth angles are not exposed to a side force from the wind.

In order for the cross hairs to reflect this correction angle Al for the target Tl, the V hair would have to move to the right of the true center of the periscopic field. If the turret is now turned so that the V hair intersects the target on the periscopic field, the guns will now lead the target Tl a correct amount so that the wind will blow the bullets to hit target Tl squarely. It will be realized that this V hair movement must be very small on a non-magnified field, and that the actual correction angles involved are very minute.

Also shown in Figure 12 is the target airplane T2, to the left of the airplane [00. As with the case of target Tl, the guns of the turret must lead plane T2 so that when the wind blows the bullets backward they will strike the plane T2 squarely. In order to reflect this correction in the periscope, the V hair will have to move to the left of the center of the field to enable the guns to lead the plane T2, rather than move to the right as was the case with target Tl. This difference in direction of movement must be indicated and for present purposes we can call the movement to the left of center positive and movement to the right of center negative. The change in sign is expressed by the radial distance from the range line CI to the 90 zenith line C2. On the 0 to 180 part of the azimuth circle these radial distances are inside the range line Cl or negative, and from 180 to 0 the distances are on the outside of the range line Cl or positive.

If a target airplane were flying on the range circle CI at 135 zenith instead of 90, the corrections will vary but slightly. The corrections for 90 and 135 zenith are nearly similar because there is little difference in the angle at which the wind strikes the bullets. The chief difference at 135 zenith is near 0 and 180 azimuth where the spinning bullet is exposed to a side wind causing a magnus eifect which diverts the bullet to the left at 0 azimuth with reference to Figure 12, and diverts the bullet to the right at 180 azimuth with reference to Figure 12. The angular correction at any point in azimuth for 135 zenith is the radial distance between the 135 zenith line, C3 and the range line Cl.

The 90 zenith line C2 and the 135 zenith line C3 are so close together, that for practical purposes a common line can be drawn between them which will adequately represent both lines. Accordingly a single composite line C4 is drawn to represent both the 90 and the 135 line for all points in azimuth. This line is drawn in most places between the two lines. The greatest divergence of the composite line C4 from the mean of lines C2 and C3 is near 180 azimuth where the composite line C4 follows the 90 line closely. This is to render the firing at the tail area near 90 zenith as nearly accurate as possible because this is .a vital area.

The actual correction therefore between zenith and zenith is incorporated in the composite line C4. The corrections at any point in azimuth are indicated by the radial lines (between the composite line C4 and the range line 01. The sign of the correction is indicated by the nature of the radial lines. On the left part of Figure 12 between azimuth and 0 azimuth, the positive correction is shown by solid lines; on the right part of Figur 12, the negative correction between 0 azimuth and 180 is shown by broken radial lines.

The composite line C4 is not an irregular curve, but rather a curve made up of arcs having the same radius as the range circle Cl. One arc is from 0 azimuth to 45 azimuth and is negative, another from 45 to 90, another from 90 to 118, another from 118 to 157, another from 157 to 237, which crosses the range line C l from negative to positive, another is from 237 to 270, still another from 270 to 319, and finally one from 319 to 0. If the composite 90 and 135 line 04 were plotted on rectilinear coordinate paper, plotting degree azimuth against correction angles, the arcs would show up as straight lines as will be described with relation to Figure 14.

The lateral deflections for 180 zenith are shown in Figure 14. In the middle part of the figure are shown the periscopic fields for the various azimuth positions when the guns are pointed at 180 zenith. The central dot DC appears in the middle of the field and marks the position toward which the guns are pointed. Wind will blow the bullets backward however, and magnus efiect will cause the bullet to deflect to th left with reference to the dot DC, to hit the target airplane in the periscopic field. This deflection is constant in amount and direction relative to the airplane I00, regardless of rotation of the turret in azimuth, because the bullets are all exposed to the same wind forces when shooting straight down.

The V and H cross hairs at all positions in azimuth must intersect at the point at which the bullets hit when the guns are pointed at 180 zenith. For purposes of illustration a target airplane is shown in this position, and for purposes of illustration its size at 600 yards range is greatly exaggerated with relation to the field, which is a 45 field. The orientation dot DT is shown on field vertically above central dot DC. When the turret is pointed at 0 azimuth, the V hair is to the left of true center (shown by the dot DC) by an amount sufflcient to compensate for the magnus effect. Although the H hair will be discussed later, it will be noted that it is below true center by an amount sufficient to compensate for wind blow. The correction of the V hair, which compensates for lateral deflections, is shown on a curve C5 to the left of the field illustrations, wherein the ordinate represents degrees azimuth and the abscissa represents the deflection angle. Since movement of the V hair to the left of center is a positive correction, this movement is marked positive (-1-) on the curve. Thus for 0 azimuth the abscissa is a small plus quantity.

At 45 azimuth the V hair must move to the right of center, or in a negative direction to intersect the target. This movement is shown on the curve C5 by a large negative deflection. At 90 azimuth the V and H hairs are interchanged as compared to the 0 azimuth positive. In this position the V hair movement reaches its greatest negative correction and this is reflected by a negative high point on the curve C5. At 135 azi- 15 muth the V hair is still at a negative correction but of slightly less amount than at 90.

When the turret is rotated to 180 azimuth, the V hair again assumes a azimuth position as at 0 azimuth, but of reverse sign. This correction is reflected on the curve as a negative correction of an amount equal to that at 0 azimuth. The correction is negative because it is to the right of center using th orientation dot DT a basis. At 225 azimuth the V hair must move to the left of center to intersect the target, a positive correction. Thus the curve C will cross the zero deflection line from negative to positive between 180 and 225 azimuth.

At 270 azimuth the V hair reaches its greatest positive deflection, reflecting the full wind blow of the bullet. At 315 the correction is still positive but smaller in amount than at 270 azimuth. From a consideration of the V hair movement as the turret turns in azimuth, with relation to the fixed deflection, it will be apparent that the curve C5 is a sine curve.

For purposes of comparison, the composite curve C4 of Figure 12 may be drawn on the same azimuth-deflection axes as the curve C5 of Figure 14. As explained with reference to Figure 12, the composite curve C4 is not an irregular curve, but a series of regular segments. These show up on Figur 14 as straight line lengths plotted at the azimuth position noted in Figure 12. It can be seen that the composite curve C4 follows the curve C5 so closely that at 180 elevation, the composite adequately represents the true curve of the V hair movements.

From the foregoing it is evident that the composite curve C4 adequately represents V hair movements at 90 zenith, 135 zenith, and at 180 zenith. Further, it can be assumed with reasonable safety, that the curves in intermediate zenith positions correspond closely to the composite curve C4 for any given position in azimuth. This being true, all that remains is to produce a voltag curve corresponding to the curve C4, and impress this voltage on the galvanometer rotor 3T2 governing the V hair movement.

An electrical cam for producing a composite curve voltage wave is shown in Figure 13. To obtain positive voltages and negative voltages corresponding with the positive and negative correction angles, there is provided a source of positive and a source of negative voltage with reference to a source of zero voltage. This can be obtained by tapping the ends of a battery for the positive and negative voltage and tapping a midpoint in the battery for the zero source as will be described later.

Figure 13 shows a series of bridges for producing a voltage curve corresponding to the azimuth composite curve C4 for the lateral deflection, and will be referred to as the lateral composite or LC cam. For illustration, the voltages of 1.5 volts and of 1.5 volts are taken as the maximum voltage corrections corresponding to the maximum angular corrections, which are practically equal though opposite in sign as at 90 and 270. Positive voltage is supplied to the LC cam by wire 54 which is connected to a supply wire 51 supplying voltage and current to the various positive cam angles at the ends of arc segments of the composite curve C4 of Figure 12; namely 237, 270, 319 and 0 azimuth. Negative voltage and current is supplied to cam LC by a wire 53 connected to a supply wire 58 supplying the various negative cam angles at the ends of arc segments of the curve C4 of Figure 12; namely,

16 45, 118 and 157 azimuth. A zero voltage wire 52 is connected to a grounding conductor 59 which in turn is connected to resistances at all of the arc segment ending angles, both positive and negative, of the composite curve C4 of Figure 12.

The actual voltage curve is formed on a series of resistances forming a circle 60. The cam LC is stationary in the airplane and voltage is taken oil from circle 60 by a take-off arm 6| synchronized with the movement of the turret in azimuth. Thus when the turret is pointed at 0 azimuth the arm BI is at the zero degree mark on cam LC, and as the turret is rotated the arm 6| moves with it for any given number of rotations. The voltages at the various points are indicated in Figure 13. At zero degrees the .055 v. corresponds to the small positive correction angle at 0 in Figure 12. At 45 the voltage is a negative .943 v. and at 90 is negative 1.5 v. corresponding to the maximum negative correction in Figure 13. Between 157 and 237 the voltage again changes sign from negative to positive and approaches the maximum at 270 again with plus 1.5 v.

The voltage circle 60 is formed by a series of simple bridges, and for purposes of illustration the formation of the voltage points at 270 and 319 will be described. At 319 the voltage drops from plus 1.5 v. in wire 51 to zero at wire 59. All that is necessary is to place a resistance between these two wires, and pick off an intermediate point on the resistance giving plus 1.106 v. A resistance R6 of 52.6 ohms connecting Wire 51 and the voltage point gives the correct voltage of 1.106 v. when in series with a resistance R"! of 152 ohms connecting the voltage point and ground wire 59. This can be approximated mathematically by multiplying the fraction R! over the quantity R6 plus R! by the maximum voltage 1.5 v., which equals 1.116.

The same considerations obtain at the 270 point. Since the maximum voltage of 1.5 v. is desired at the voltage point a conductor 62 leads from wire 51 to the voltage point. A resistance R9 is connected between the 270 voltage point and ground wire 59 and is approximately equal to the sum of the radial resistances connected at any voltage point or about 200 ohms. A resistance R8 connects the voltage points of 210 and 3|9 to give a straight line graduation of voltage between the two. This resistance R8 is relatively high because the current taken off by arm BI is very small, as will be explained later. The details of calculation of the correct resistance, for circle 60 between voltage points are dependent upon resistance in the circuits supplied by arm 6|, and these calculations are well known in the electrical art and need not be explained here. The single bridge circuit just described is duplicated between all other supply points on the circle 60 and by connecting the whole together the voltage circle 60 is formed. In this manner an accurate voltage wave may be formed for the composite curve LC, and yield voltages at any point in azimuth which are satisfactory for all points in zenith from 90 to 180.

Vertical ballistics correction The correction angles for the vertical ballistics deflection of a bullet are shown in Figure 16. The airplane H10, in which the lower turret is mounted is shown in the center of its hemisphere of fire. The range line for 90 zenith is shown as line C6. The correction angles for any point in azimuth 

